Question 1

How hard are these hard sudoku puzzles?

Accepted Answer

Scanning alone will stall. Finishing these means keeping candidate notes and spotting pairs — two cells in a unit that can only hold the same two numbers, which rules those numbers out elsewhere. Each of the 12 puzzles in this set starts from about 28 given numbers.

Question 2

Does every puzzle have only one solution?

Accepted Answer

Yes, and that is checked rather than assumed. Clues are removed one at a time, and after each removal the puzzle is re-solved to confirm exactly one solution remains. If a removal would create a second solution, the clue goes back. A puzzle with two answers is not a harder puzzle — it is a broken one.

Question 3

Is there an answer key?

Accepted Answer

Yes. The last two pages of the PDF hold all 12 solutions, six to a page.

Question 4

Do I need to guess?

Accepted Answer

Never. Every puzzle here is solvable by logic alone. If you find yourself guessing, there is a deduction still available somewhere on the grid.

Question 5

Are these the same puzzles every time?

Accepted Answer

Yes. Each puzzle is generated from a fixed seed, so the file you download today is the same one you would download next year — which means a printed answer key never stops matching its puzzles.

empty	5	3	8	empty	empty	2	empty	empty
empty	empty	empty	empty	empty	empty	empty	empty	1
7	1	9	empty	2	empty	5	empty	6
empty	empty	6	empty	empty	empty	empty	empty	5
8	4	empty	2	5	empty	empty	empty	9
empty	empty	5	empty	3	empty	empty	empty	empty
empty	empty	empty	empty	empty	empty	empty	empty	empty
5	empty	empty	empty	empty	3	empty	empty	4
empty	empty	1	7	6	empty	empty	2	8

12 hard sudoku puzzles, with answers.

Puzzle 1 from this set

What makes these hard

Every puzzle has exactly one solution

Other difficulties

Common questions

Printing